Portland's Adult Soap Box Derby offers few rules about building your car. If it has at least three wheels, no propulsion and functioning brakes, it's probably good to go.

That opens the floodgates to Portland's eccentric creative types, who jump every year at the opportunity to create something fun and functional on the fly. The results are predictably incredible, ranging from sleek vehicles that fly 41 mph to a giant transgender Potato Head.

The crews have nearly four months to craft their cars – that's the deadline for conceptual sketches – but many apparently spend that time talking and thinking rather than actually building.

"This is a seven-day build," said Seamus Holley, representing a team from Portland craft and design collaborative ADX, who built a car called "Falcon Arrow 5000." "The design parameters kind of flew out the window at a certain point and we just started letting pieces fall together, and they did magically somehow start falling together."

The story was similar at the crew responsible for the "Shame of Thrones" car. The idea was built on a play on words, they said, but then transformed into a concept where "Game of Thrones" houses were represented by "shameful" beers – Pabst, Hamms, Tecate and Miller High Life. They used those cardboard beer cases to craft armor and flags for each house. They modeled their car after the show's infamous Iron Throne.

"We started from a frame on Sunday," one crew member said. "I mean I've been creating swords for a number of weeks," noted another. "We talk about it for about three months and then we come down to like a week before and put it all together," admitted a third.

But not all crews had such hasty execution. Some put much time, thought and effort into building their cars.

Take Gary Apple, a racer from California, for example. He brilliantly crafted a giant Mr. Potato Head on a red wagon, with detachable parts that could transform him into a Mrs. Potato Head in between heats.

"It was just something to do," Apple said. "When you're retired you do stupid things like this."

The Californian said he loves Portland's Adult Soap Box Derby, so much so that he and a group in his hometown of Nevada City have started one of their own, modeled after what he called "the mothership of soap box racing" in Portland.

The crowds seemed to like it as well. Swarms of people gathered along the winding race course at Mt. Tabor Park on Saturday morning, lining the sides of the paved road with blankets, kids, pets and some with entire picnics.

The crowd shuffled every few minutes between heats, scurrying from one vantage point to another up the road as volunteers with megaphones urged them to hurry to their places and to stand ten feet back from the course.

The crowds roared as cars cruised through. Some whizzed by too fast to really see, while those competing in the creative class rolled by slowly, like parade floats designed (apparently) to race.

Crowd favorites included a mockup of the RV from "Breaking Bad" (complete with blue candy), a rolling red light district with scantily-clad men in drag, and that impressive transgender Potato Head.

"It's just about the fun challenge. We've never done it before," said Joe Freitas, creator of the "Breaking Bad" RV. "We're just out here to have fun and put a smile on people's faces."